Various techniques have been devised to increase the transmission capacity of a wireless access system (hereinafter which may also be referred to as the “system capacity”). For example, there is a technique available to increase the system capacity by providing a femto-base station for forming a small communication area of about 10 meters in radius in addition to a macro base station for forming a large communication area which is several hundreds of meters to several kilometers in radius. Here, the “communication area” is defined as the area which the radio waves transmitted from the base station cover at predetermined power or greater. For example, the macro base station is capable of transmitting at high transmission power, whereas the femto-base station transmits at low transmission power. Furthermore, for example, implemented in the macro base station unit is the function of a base station for forming a communication area by the 3G communication scheme (hereinafter which may also be referred to as the “3G base station”). On the other hand, for example, implemented in the femto-base station unit may be the function of a base station for forming a communication area by the 3G communication scheme and the function of a base station for forming a communication area by the WiFi communication scheme (hereinafter which may also be referred to as the “WiFi base station”). Hereinafter, the communication area formed by the 3G communication scheme will also be referred to as “the 3G area,” while the communication area formed by the WiFi communication scheme will also be referred to as “the WiFi area.” Furthermore, the communication system for performing communications by the 3G communication scheme will also be referred to as “the 3G system,” while the communication system for performing communications by the WiFi communication scheme will also be referred to as “the WiFi system.” That is, the 3G system forms the 3G area, while the WiFi system forms the WiFi area. Note that the WiFi base station may also be called “the WiFi access point.”
The communication terminal having both the communication functions of the 3G and the WiFi switches the destination, to which the communication terminal is connected, from the 3G system to the WiFi system upon entry to the WiFi area, while switching the destination, to which the communication terminal is connected, from the WiFi system to the 3G system upon exit from the WiFi area. Such switching of the destination to which the communication terminal is connected may be called the “handover.” The switching of the destination, to which the communication terminal is connected, from the 3G system to the WiFi system is not originated by the control provided from the 3G network but driven by the communication terminal.
[Patent Document 1] International Publication Pamphlet No. WO2010/110216
[Patent Document 2] Japanese Laid-open Patent Publication No. 2010-004458
[Patent Document 3] Japanese Laid-open Patent Publication No. 2012-208885
The communication terminal in the wireless access system has mobility when compared with the wired communication terminal, so that even when having entered a communication area, the communication terminal may exit the communication area in a short time. For example, suppose that a communication terminal user buys takeout goods at a fast-food restaurant or the like at which a WiFi base station is provided to form a WiFi area or an example communication area. In this case, the user may exit the WiFi area or the restaurant in a short time. Furthermore, the communication terminal moving near the boundary of the WiFi area may exit the WiFi area in a short time after having once entered the WiFi area. In such a case, the destination to which the communication terminal is connected is once switched from the 3G system to the WiFi system, and in a short time after that, the destination is switched from the WiFi system back to the 3G system. That is, the RAT switching such as handover occurs frequently. Frequent occurrence of handover between communication systems that employ different communication schemes may lead to increases in the exchange of control signals for ending or starting connections, causing increases in communication traffic. Furthermore, since seamless handover is not ensured between communication systems employing different communication schemes, frequent occurrence of handovers may lead to degradation in data quality due to increases in data loss or the like.